1. Field of the Invention
The present invention relates in general to methodologies for the treatment quenching preconditioning and communication between the intrinsic cardiac nervous system and an electrical stimulus. In particular, the present invention utilizes spinal cord stimulation to alter and/or affect the intrinsic cardiac nervous system and thereby protect the myocytes, stabilize myocardial electrical instability and/or alleviate or diminish cardiac pathologies.
2. Brief Description of the Field of the Invention
Recently, the emergence of novel views of the anatomic pathways and neural mechanisms involved in the regional control of the heart have led to the presently claimed and disclosed intrinsic cardiac nervous system modalities and treatments. In fact, it has been determined that a level of processing occurs that permits independent intrinsic cardiac as well as intrathoracic extracardiac and central spinal integration of afferent and efferent autonomic influences, and local neural coordination without necessarily involving the higher brain centers. This knowledge has led to the development of the presently claimed and disclosed invention(s). Lathrop and Spooner [24] have postulated that a “hierarchy of control mechanisms among these different elements, and that they interact as a system of autonomous efferent feedback loops rather than simply as relay stations subservient to central command.” Indeed, disruption of neuronal circuitry leads to numerous cardiac pathologies. Neuronal interactions that occur within this circuitry or hierarchy modulate different regions of both healthy and diseased hearts. Thus, the knowledge of this circuitry and methodologies of modulating this circuitry (as disclosed and claimed herein) have allowed for the development and treatment of cardiac pathologies using novel therapeutic approaches to ameliorate specific cardiac pathologies.
Regional control of cardiac function is dependent upon the coordination of activity generated by neurons within intrathoracic autonomic ganglia and the central nervous system. The hierarchy of nested feedback loops therein provides precise beat-to-beat control of regional cardiac function. Contrary to classical teaching, studies undertaken and disclosed in the present specification utilizing electrophysiological and neuropharmacological techniques applied from the level of whole organ to that of neurons recorded in vitro indicate that intrathoracic autonomic ganglia act in a manner greater than simple relay stations for autonomic efferent neuronal control of the heart. It has been determined that within this hierarchy of intrathoracic ganglia and nerve interconnections, complex processing takes place that involves spatial and temporal summation of sensory inputs, preganglionic inputs from central neurons and intrathoracic ganglionic reflexes activated by local cardiopulmonary sensory inputs. The activity of neurons within intrathoracic autonomic ganglia is likewise modulated by circulating hormones, chief among them being circulating catecholamines and angiotensin II.
The progressive development of cardiac disease is associated with maladaptation of these neurohumoral control mechanisms. Recent data indicate that conventional therapy of cardiac diseases such as myocardial ischemia and heart failure exert their beneficial effects not only on cardiomyocytes directly, but indirectly via the intrinsic cardiac nervous system. The presently disclosed and claimed inventions of the complex processing that occurs within the intrathoracic nervous system, as well as between peripheral and central neurons, will provide a basis for understanding the role that the cardiac nervous system plays in regulating not only the normal heart, but the diseased heart. Information derived from research and experimentation of this complex neuronal hierarchy provides for novel therapeutic approaches for the effective treatment of cardiac dysfunction including protection of cardiac myocytes and stabilization of myocardial electrical activity by targeting various populations of neurons regulating regional cardiac behavior.
Varying elements within the cardiac neuronal hierarchy exert more influence over regional cardiac function than has been traditionally understood. For example, it is now well recognized that the cardiac nervous system is fundamental to the management of heart failure. As such, this nervous system represents a novel and previously unrecognized target for the treatment of heart failure. Control of regional cardiac function is dependent upon intrinsic properties of the cardiac electrical and mechanical tissues as modulated by neural inputs arising from neurons in the intrathoracic autonomic ganglia, spinal cord and brainstem. Disruptions in neural inputs to the heart or alterations in the cardiac interstitial milieu can be associated with deleterious cardiac structural remodeling and, as a consequence, cardiac dysfunction. In the most extreme case, this becomes evident in congestive heart failure. Excessive activation of the intrathoracic cardiac efferent nervous system, as with myocardial ischemia, can evoke ventricular dysrhythmias involving changes within the cardiac nervous system in addition to alterations in cardiomyocyte ion channel function. Maladaptation of neurohumoral control mechanisms can likewise adversely remodel the cardiac extracellular matrix.
The conventional treatment for reducing the frequency and intensity of angina pectoris resulting from myocardial ischemia is anti-ischemic therapy. These therapies are usually based upon restoring the balance between myocardial oxygen supply and myocardial oxygen demand. Pharmacological agents and revascularization procedures (CABG and PTCA) are conventional treatments for such disease states. Yet there are a significant number of patients that do not experience adequate relief of their anginal symptoms with these treatments or are poor candidates for these therapies. Thus, alternative approaches utilizing direct electrical activation of neural elements within the spinal cord have been devised, with the resultant modulation of the intrathoracic neurohumoral milieu thereby eliciting anti-ischemic, antiarryhtymic, and anti-anginal effects.
A disturbance of the fine balance within the whole cardiac neuraxis can result in dramatic changes in cardiac efferent neuronal outflow. Experimental studies have been performed to demonstrate that pathological processes can change the integrative behavior of the cardiac neuraxis. These changes occur when cardiac sensory neurites are activated intensely and for long periods, as when cardiac tissue becomes damaged during regional ventricular ischemia. On the other hand, central processing of cardiac sensory output may become deranged leading to conflicting signals that interfere with the maintenance of cardiac function. This has led to the proposed scheme that the hierarchy of cardiac neurons interacts effectively if there is an appropriate balance therein.
Under normal, physiological conditions stimuli applied to the heart do not elicit marked changes in cardiac efferent neuronal activity because central neurons can suppress excessive cardiac sensory information processing. Information has been obtained to support the conclusion that, in the hierarchy of cardiac control, activation of spinal neuronal circuits modulates the intrathoracic cardiac nervous system. Experimental studies have shown that activation of the dorsal columns at the T1-T2 segments significantly reduces the activity generated by the intrinsic cardiac neurons in their basal conditions as well as when activated in the presence of focal ventricular ischemia induced by occluding the left coronary artery. Not only does dorsal column activation modulate the intrinsic cardiac nervous system, but it also modifies the activity of spinal neurons within the T3-T4 segments. In addition, experimental evidence indicates that the central nervous system maintains a tonic inhibitory influence over intrathoracic cardiopulmonary-cardiac reflexes. One of the present inventors has also shown that reflexes mediated through the middle cervical ganglion are increased after decentralization. Based on this evidence, it is postulated that disease processes change the balance between the central and peripheral neuronal processing of cardiac sensory information. Thus, use of electrical currents to activate spinal neuronal circuits can reverse or halt disease processes of the heart preconditioning the heart—i.e., applying electrical activation prior to disease—also is contemplated as a means to pro-actively treat a patient with high susceptibility to cardiac pathologies including arrhythmias.
Within the hierarchy for cardiac control, neurons of the upper cervical segments modulate information processing in the spinal neurons of the upper thoracic segments. In human studies, spinal cord stimulation of the C1-C2 spinal segments relieved the pain symptoms in patients with chronic refractory angina pectoris. Experimental studies in support of the presently claimed and disclosed invention have shown that spinal cord activation of the upper cervical segments of the spinal cord suppressed the activity of spinal neurons in T3-T4 segments. Furthermore, chemical stimulation with glutamate of cells in the C1-C2 segments also reduced upper thoracic spinal neuronal activity. The upper cervical region is intriguing because it is positioned between supraspinal nuclei and spinal circuitry. Neurons in C1-C2 could serve as a filter, an integrator, or as a relay for afferent information, since these neurons receive inputs from vagal afferents from the heart.
Very little information has been published to address underlying mechanisms explaining how central and peripheral cardiac neurons process cardiac sensory information and interact in the maintenance of adequate cardiac output. The presently claimed and disclosed invention shows that disease processes change the balance between the central and peripheral neuronal processing so involved. For instance, when the activity generated by cardiac sensory neurons becomes excessive (such as during focal ventricular ischemia), cardiac function is profoundly affected, cardiac myocyte protection is reduced and arrhythmias are increased. A disturbance of the fine balance within the whole cardiac neuraxis results in dramatic changes in cardiac efferent neuronal outflow. Over the past 30 years, the anatomy and function of the peripheral cardiac nervous system has been studied, focusing during the last decade on its intrinsic cardiac component. The classical view of the autonomic nervous system presumes that its intrinsic cardiac component acts solely as a parasympathetic efferent neuronal relay station in which medullary preganglionic neurons synapse with parasympathetic efferent postganglionic neurons therein. In such a concept, the latter neurons project to end effectors on the heart with little or no integrative capabilities occurring therein. Similarly, intrathoracic extracardiac sympathetic ganglia have been thought to act solely as efferent relay stations for sympathetic efferent projections to the heart. As the presently claimed and disclosed invention shows, neural control of regional cardiac function resides in the network of nested feedback loops made up of the intrinsic cardiac nervous system, extracardiac intrathoracic autonomic ganglia, the spinal cord and brainstem. Within this hierarchy, the intrinsic cardiac nervous system functions as a distributive processor at the level of the target organ. Thus, the intrinsic cardiac nervous system plays an important role in the functioning of the heart and in its diseased pathologies. This novel information thereafter leads to numerous methodologies (some of which are claimed and disclosed herein for the treatment, preconditioning and/or quenching of disease pathologies through the use of spinal cord stimulation.
Experimental studies have also shown that pathological processes can change the integrative behavior of the cardiac neuraxis. These changes occur when populations of cardiac sensory neurites are activated intensely and for long periods of time when local cardiac tissue becomes damaged during, for instance, regional ventricular ischemia. Thus, under normal, physiological conditions stimuli applied to the heart do not elicit marked changes in cardiac efferent neuronal activity because central neurons suppress cardiac sensory information processing. On the other hand, central processing of cardiac sensory output may become deranged during excessive inputs leading to conflicting signals that interfere with the maintenance of cardiac function. This has led to the novel concept that the hierarchy of cardiac neurons interact effectively if there is an appropriate balance therein. Fundamental to this hierarchy is its component on the target organ—the intrinsic cardiac nervous system and its influence on the heart.
Consistent coherence of activity generated by differing populations of neurons is indicative of principal and direct synaptic interconnections between them or, conversely, the sharing by such neurons of common inputs. Such relationships have been identified among medullary and spinal cord sympathetic efferent preganglionic neurons, as well as among different populations of sympathetic efferent preganglionic neurons. Different populations of neurons, distributed spatially within the intrinsic cardiac nervous system, respond to cardiac perturbations in a coordinate fashion. If neurons in one part of this neuronal network respond to inputs from a single region of the heart, such as the mechanosensory neurites associated with a right ventricular ventral papillary muscle, then the potential for imbalance within the different populations of neurons regulating various cardiac regions might occur and, thus, its neurons display little coherence of activity. In other words, relatively low levels of specific inputs on a spatial scale to the intrinsic cardiac nervous system result in low coherence among its various neuronal components. On the other hand, excessive input to this spatially distributed nervous system would destabilize it, leading to cardiac arrhythmia formation, etc.
Thus it is an object of the present invention to use the identification of the intrinsic cardiac nervous system along with the experimental data and results to provide methodologies utilizing spinal cord stimulation for the (1) treatment of cardiac disease pathologies; (2) communication between an external point and the intrinsic cardiac nervous system; (3) preconditioning of the intrinsic cardiac nervous system in order to promote a protective effect against cardiac disease pathologies; and (4) quenching aberrant neuronal activity occurring within the intrinsic cardiac nervous system.
This and numerous other objects of the present invention will be appreciated in light of the present specification, drawings, and claims.